Comparisons of Global Heat Transfer Correlations for Conventional and High Efficiency Reciprocating Engines

Abstract

Cylinder wall heat transfer is known to be an important process for internal combustion engines, and directly affects engine efficiency, performance and emissions. In some cases, up to third of the fuel energy is lost via heat transfer. Better understandings of the cylinder heat transfer should provide opportunities for improvements of engine efficiency and performance. The influence of various heat transfer correlations on engine efficiency and performance, total heat transfer and nitric oxide emissions is determined for conventional and high efficiency engines. These high efficiency engines are often based on “low temperature combustion” — and such engines have inherently lower heat transfer. At least some of the improvements associated with LTC engines are attributed to reduced heat losses. This work uses a thermodynamic engine cycle simulation and studies automotive engines. Both conventional and LTC engines are examined. As expected, engine performance and efficiency increase for reductions in the cylinder wall heat transfer. Although the heat transfer is lower for LTC engines compared to conventional engines, efficiency increases still are obtained as the cylinder wall heat transfer is reduced. In addition to the above, these assessments include the effects of the various heat transfer correlations on nitric oxide emissions and exergy destruction during the combustion process for both engines.